1. Field of the Invention
The present invention relates to photosensitive compositions.
Compositions comprising vinyl alcohol polymers, radically polymerizable ethylenic unsaturated compounds (hereafter referred to as polymerizable monomers) and photopolymerization initiators are termed photosensitive compositions and have been widely used as, for example, plate-making materials for letterpress plate.
2. Description of the Prior Art
The aforesaid photosensitive compositions are formed into a sheet form (termed photosensitive resin plate) on a support such as a metal plate or film plate, then exposed to light and developed to make resin plate-making materials. Photosensitive compositions using vinyl alcohol polymers have been widely used in the printing art because unhardened regions can be readily dissolved out with water after exposure to make Printing operation easy ( Published Examined Japanese Patent Application Nos. 39401/71 and 3041/75).
As described above, currently used photosensitive compositions comprising vinyl alcohol polymers are advantageous in many aspects and are used in large quantities as materials for pattern plates particularly because surface hardness of plate-making resins is high.
However, resin plates of vinyl alcohol polymer type are generally inferior in flexibility and impact resistance so that there is often caused a phenomenon that the resin plates are broken, etc. upon printing particularly in winter season where temperature and humidity are low, and such comes into a serious question. Further due to great changes in circumstances of printing technology in recent years, high quality of printed characters is required also for vinyl alcohol polymer resin plates.